Miniaturization in semiconductor manufacturing technology has been progressing in recent years with state-of-the-art processes now adopting line widths of 20 nm and even 10 nm. Since this miniaturization in the field of semiconductor manufacturing technology has been accompanied by increased technical difficulty in processing, techniques are being developed using various approaches in terms of used materials, equipment, processing methods, and so forth.
Against this background, the applicant has carried out diligent research in relation to dry etching gases that are also suitable for use in state-of-the-art dry etching processes. The applicant discovered that a saturated hydrofluorocarbon represented by CxHyFz (x represents 3, 4, or 5; y and z each represent a positive integer independently of one another; and y>z), such as 2-fluorobutane, has superior performance to monofluoromethane used in etching of silicon nitride films (PTL 1).
A number of conventional methods for producing 2-fluorobutane are known.
PTL 2 discloses that 2-fluorobutane was obtained with a yield of 46% by bringing N,N′-diethyl-3-oxo-methyltrifluoropropylamine (fluorinating agent) into contact with 2-butanol. PTL 3 describes bringing sulfur hexafluoride into contact with sec-butyllithium cyclohexane/hexane solution to obtain sec-butyl fluoride.
PTL 4 describes a method of producing 2-fluorobutane by bringing 2-butanol and a fluorine-containing ylide into contact in the presence of 2-butene. PTL 5 describes hydrogenating 2-fluorobutadiene in the presence of a catalyst to obtain 2-fluorobutane.
In PTL 6, high-purity 2-fluorobutane is obtained by performing distillation, drying, and denitrification/deoxygenation with respect to crude 2-fluorobutane obtained by a reaction step.
However, although methods for producing 2-fluorobutane are described in these conventional techniques, hardly any information is provided about the purity of the obtained 2-fluorobutane or impurities therein, and a method for efficiently purifying 2-fluorobutane is not described.
NPL 1 and 2 describe methods for obtaining a dihalopropane product through addition of dihalocarbene to an olefin. In the method described in NPL 1, cis-/trans-butene is reacted with bromoform and potassium t-butoxide to obtain a dibromocyclopropane product. In the method described in NPL 2, cyclohexene and isobutene are reacted with chloroform and potassium t-butoxide to obtain a dichlorocyclopropane product.